1. Field of the Invention
The present invention relates to a data input device such as a keyboard having the function of releasing accumulated static electricity on a human body.
2. Description of the Related Art
With the recent development of data processing apparatuses, keyboards are increasingly used as data input devices for transferring data between people and machines. Keyboards have multiple data input keys that are operated by hand to input data represented on the keys into the machine.
Static electricity frequently accumulates on an operator and, when an operator with static electricity accumulated thereon touches a keyboard, a discharge occurs between the operator and the keytop and a noise is produced in an electric circuit in the keyboard or in the computer, and if the noise is large, the computer may work incorrectly or stop. Accordingly, there is an arrangement such that a portion of the keyboard that is assumed to be first touched by an operator is connected to a ground so as to release static electricity to a ground when the operator touches that portion.
For example, Japanese Unexamined Utility Model Publication (Kokai) No. 59-62699 discloses an electronic device having a switch, in which a portion of the switch assumed to be touched by an operator is made from an electrically conductive material and a metal piece is provided so as to slidably engage with a movable portion of the switch with the metal piece connected to a ground via resistance.
Also, Japanese Unexamined Patent Publication (Kokai) No. 60-97420 discloses a keyboard in which a keytop is made from an electrically conductive material that is connected to a ground by a conductor wire. Also, in a modification in this reference, a stationary key holder facing the movable keytop is connected to a ground so that the keytop is brought into contact with the key holder so as to release static electricity to the ground when the keytop is operated.
Also, a recent Japanese patent application filed by the assignee of this application proposes a keyboard having a link displaceably connecting a keytop with respect to a support panel, in which the keytop is electrically connected to the support panel via the link so as to release static electricity to a ground via the support panel.
In this way, it is possible to release static electricity to the ground, by connecting a portion of the keyboard that is to be touched by the operator to the ground. However, there are problems in the above described prior arts. In the prior art stipulating that the keytop of the keyboard be directly connected to the conductor wire, there are problems in the wiring and the key operating facility. In the prior art stipulating that the keytop of the keyboard is slidably engaged by the metal piece that is not a fundamental element of the key, there are problems in the key operating facility and there is bad electrical contact between these elements, thereby making it impossible to release static electricity. Also, in the prior art stipulating that the keytop be brought into contact with the key holder when the keytop is operated, it is impossible to release static electricity reliably because it is not certain that the keytop contacts the key holder when an operator touches the keytop lightly.
When static electricity accumulated on a person is released to the ground, a discharge current flows. If the discharge current is too high, the operator experiences an electric shock. Accordingly, it is necessary to arrange a resistance between the keytop and the ground for controlling the discharge current at an appropriate value. In this case, when the resistance is too high, it is impossible to properly release static electricity. Accordingly, the Sweden ESD Standard, for example, stipulates that resistance in the static electricity releasing circuit between the keytop and the ground be within a range from 10 to 500 M.OMEGA..